The present invention relates to a piezoelectric/electrostrictive device comprising a movable portion to be operated by displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device capable of detecting displacement of a movable portion by a piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in mechanical strength, impact resistance, and humidity resistance, and is capable of having the movable portion efficiently operated in large magnitude.
In recent years, in the fields of optics and magnetic recording, precision machining, and the like, a displacement element capable of adjusting an optical path length or position in sub-micron order has been required, and development has been progressed of a displacement element utilizing a displacement due to the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied on a piezoelectric/electrostrictive material (for example, a ferroelectric substance, or the like). For example, as shown in FIG. 18, a piezoelectric actuator 21, in which, by providing a hole 28 on a plate-like body composed of a piezoelectric/electrostrictive material, a fixing portion 25, a movable portion 24, and a beam 26 connecting therewith are integrally formed, and an electrode layer 22 is further provided on the beam 26, is disclosed in JP-A-10-136665.
In the actuator 21, when a voltage is applied across the electrode layer 22, the beam 26 expands or contracts in a direction in which the fixing portion 25 is connected with the movable portion 24 by the inverse piezoelectric effect or the electrostrictive effect, thus enabling the movable portion 24 to displace in an arc-shaped mode or a rotational mode in the plane of the plate-like body. On the other hand, JP-A-63-64640 discloses a technique with regard to an actuator utilizing a bimorph, wherein an electrode of the bimorph is split to be provided thereon, and the actuator is driven by selecting the split electrodes to perform precise positioning at a high speed, and for example, a structure in which two bimorphs are used mutually opposing is shown in FIG. 4 of the specification thereof.
However, with the actuator 21, as a displacement in the expansion/contraction direction (namely, the in-plane direction of the plate-like body) of the piezoelectric/electrostrictive material is transmitted per se to the movable portion, there is a problem that an operational quantity of the movable portion 24 is small.
Further, the actuator 21, having all members thereof composed of a piezoelectric/electrostrictive material, which is fragile and relatively heavy in weight, has further problems, in addition to the mechanical strength being low, and being inferior in handling property, impact resistance, and humidity resistance, in that the actuator 21 per se is heavy and is likely to be influenced by harmful vibrations (for example, residual vibrations or noise vibrations when operated at a high speed) in operation. In order to solve the above-described problems of the actuator 21, a proposition is made that the hole 28 is filled with a filler having flexibility. However, it is apparent that the efficiency of the displacement due to the inverse piezoelectric effect or the electrostrictive effect is decreased, when the filler is used.
On the other hand, what is shown in FIG. 4 of JP-A-63-64640 is that, in joining an intermediary member 3 with a bimorph, a portion having no divided electrode is joined with the intermediary member, and at the joined portion, only a bimorph portion unable to utilize an effect of the divided electrode, namely a bimorph portion which is not a displacement generator is joined. On the other hand, the joining at a joined portion of a head with a bimorph is in the similar joining mode. As the result, the bending displacement of the bimorph is developed toward the inner space between the intermediary member and the head, and it is a structure where an action for effectively displacing the head per se toward the outer space is unable to be obtained. In addition, the actuator disclosed in JP-A-63-64640 is so structured that a displacement generating member and a so-called frame member (intermediary member or the like) are separately prepared, and then adhered together to be incorporated, and consequently it is a structure where the joined state of the frame with the bimorph is likely to vary with time, and also drifting of a displacement, exfoliation, or the like is likely to be caused. Further, the structure having an adhesive intervened at the joined portion of a bimorph with an intermediary member and at the joined portion of a head with the bimorph, namely at a holding portion for a displacement member is also a structure where rigidity of the holding portion per se is low and it is difficult to obtain a higher resonant frequency which is required in high speed operation.
Although the present applicants have, of course, proposed a piezoelectric/electrostrictive device capable of solving such problems in the specification of the Japanese Patent Application No. 11-375581 and the like, development of a piezoelectric/electrostrictive device capable of obtaining still larger displacement quantity as well as capable of high speed response has been sought after as a precise positioning mechanism in the optical and magnetic recording fields.
The present invention is made in view of such current situation, and an object thereof is to provide a displacement element which is capable of increasing mechanical rigidity of joined portions of the thin plate portions with the movable portion and the thin plate portions with the fixing portion, facilitating higher resonant frequency, and further increasing displacement quantity of the movable portion, and a sensor element capable of efficiently detecting vibrations of the movable portion in higher precision.